Modeling results for the composition and typology of non-primary Venusian anorthosite

Anorthosite is a plutonic igneous rock composed almost entirely of plagioclase feldspar. Telluric planets may initially develop a primary anorthositic crust before lithospheric recycling processes commence. Non-primary anorthosite forms as a consequence of accumulation of plagioclase that crystallizes from basaltic or primitive mafic/ultramafic magma. Here we show that fractional crystallization modeling of parental magma compositions similar to basalt identified on Venus can yield plagioclase with anorthite contents typical of non-primary anorthosites of Earth. Using terrestrial anorthosite typology, we conclude that analogues of Archean megacrystic anorthosite, layered mafic intrusion anorthosite, and anorthosite inclusions are likely to be present within the crust of Venus. Proterozoic massif-type anorthosite, if present, would likely be restricted to the highland terranes of Ishtar Terra and Ovda Regio whereas oceanic anorthosites are unlikely to be present. Furthermore, our results indicate that the leucite-rich cumulate rock known as italite may also exist within the Venusian crust.